Leaf tip burn on cannabis: the short answer

Leaf tip burn shows as brown, yellow, or crisp tips on cannabis leaves. The usual cause is nutrient burn from a feed that is too strong or from salts that collect in the growing medium. Other triggers include pH drift, heat stress, low humidity, soggy roots, and root disease. Confirm the cause before you act, because flushing a plant that is heat-stressed or overwatered makes the problem worse.

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What leaf tip burn looks like

Damage starts at the leaf point and moves inward. Tips turn pale, then tan or brown, and the leaf edge can curl. In late flower, mild tip burn on a few sugar leaves is common and often harmless. Widespread tip burn that travels down the leaf edges points to a root-zone problem, not a light problem.

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Common causes

Nutrient burn

Too much fertilizer raises the electrical conductivity (EC) of the root zone. Water moves out of the leaf tips by osmosis, and the cells dry out. This happens with bottled nutrients, amended soil, and slow-release pellets.

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pH drift

When pH leaves the 5.8 to 6.5 range in soil or 5.5 to 6.2 in coco and hydro, some nutrients lock out while others build up. The imbalance burns tips even if the total feed strength looks normal.

cannabis nutrient burn leaves symptoms

Heat and low humidity

Temperatures above 85°F with humidity under 40% pull water from the leaves faster than the roots replace it. Tips dry and crisp. Leaves may also cup or taco upward.

Wet roots and poor oxygen

Overwatering and compacted media leave roots without oxygen. The plant cannot take up water, so leaf tips die back. This looks like nutrient burn, but the medium stays wet for days.

Root disease

Pythium, fusarium, and root aphids damage roots. The plant shows tip burn along with slow growth, drooping, and brown roots.

Salt buildup in the medium

Repeated feeding without runoff leaves fertilizer salts in the pot. The EC climbs, and tip burn appears even when you feed at the label rate.

How to diagnose the cause

  1. Measure the pH and EC of your feed water and of the runoff.
  2. Check the medium moisture 2 inches down before the next watering.
  3. Record the canopy temperature and relative humidity at leaf level.
  4. Pull one plant and inspect the roots for color and smell.
  5. Compare the pattern: even tip burn across all plants points to feed or pH, while top-canopy burn points to heat or light.

How to fix leaf tip burn

  1. Stop adding nutrients and water with plain, pH-adjusted water until runoff EC drops below 1.2 in soil or 1.0 in coco.
  2. Flush the medium with three times the pot volume of water if runoff EC is above 2.0.
  3. Reset the feed to 50% strength, then raise it in small steps over one week.
  4. Set pH to 6.0 to 6.5 in soil and 5.6 to 6.0 in coco or hydro.
  5. Keep the canopy at 75 to 82°F and humidity at 45 to 60% during veg and early flower.
  6. Water only when the top inch of medium is dry, and make sure the pot drains.
  7. Trim dead leaf tips with clean scissors, but leave the green part of the leaf.

Prerequisites for the fix